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B1.1.13—Non-polar steroids

Steroids are mostly non-polar lipids with fused carbon rings, allowing steroid hormones to interact with hydrophobic membrane interiors in cells.

Syllabus
First assessment 2025
Objective
B1.1.13
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2021
Most common paperPaper1
Typical marks1

Common command terms

  • Identify

Recent exam appearances

November 2021Paper1 ["HL"] · TZ05[ 1 ]B1.1.13—Non-polar steroids
Practice this objective

Coverage 2021–2021 · Updated 15 Jul 2026

Steroids Have a Non-Polar Hydrocarbon Core

Steroids have four fused carbon rings. Mostly non-polar steroids can dissolve in the hydrophobic core of a phospholipid bilayer and diffuse through it.

The fused-ring skeleton is dominated by C–C and C–H bonds, so it interacts more favourably with lipid tails than with water. Attached polar groups modify, but do not necessarily remove, this lipid solubility.

Oestradiol and testosterone are steroid hormones derived from cholesterol. Their bilayer permeability allows them to enter target cells, where their receptors are intracellular rather than exposed only on the cell surface.

A testosterone molecule can partition into the membrane's hydrophobic core, cross the bilayer and bind an intracellular receptor that changes cell activity.

Steroid identifies a four-ring structural family. Not every steroid is completely non-polar, and membrane passage does not mean diffusion is equally rapid for every attached functional group.

Non-polar steroids

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Identify.

Command terms

Identify

What earns marks

Build the answer around this relationship: Steroids are lipids with four fused carbon rings.

Representative question

Question 1

[Maximum number: 1]

Testosterone is a hormone that is important for male reproductive development.

To which group of compounds does testosterone belong?

A

Nucleotides

B

Carbohydrates

C

Lipids

D

Amino acids

Structure To Function

B1.1 becomes easy when every answer follows structure -> property -> function. Carbon skeletons and functional groups create molecular diversity. Condensation builds larger molecules and hydrolysis breaks them. Alpha-glucose stores energy as starch and glycogen; beta-glucose forms strong cellulose. Surface carbohydrates enable recognition. Lipids are hydrophobic, triglycerides store energy, phospholipids self-assemble into bilayers, and steroids cross membranes because they are mostly non-polar.

  • Carbon bonding and functional groups explain molecular diversity.
  • Condensation releases water; hydrolysis uses water.
  • Carbohydrates can store energy, build cell walls, and mark cell surfaces.
  • Lipids are hydrophobic and not true polymers.
  • Triglycerides store energy; phospholipids form membranes; steroids signal across membranes.

Concept essentials

  • Steroids are lipids with four fused carbon rings.
  • Steroid molecules are mostly non-polar.
  • Testosterone and oestradiol are steroid hormones.
  • Non-polar steroid hormones can interact with hydrophobic membrane interiors.